1. Field of the Invention
The present invention relates to a discharge energy recovery device and an image forming apparatus employing the discharge energy recovery device.
2. Description of the Background Art
Some image forming apparatuses print images on recording media by jetting ink droplets, in which a piezoelectric element (hereinafter, also referred to as an actuator) is driven when supplied with a given voltage and a large number of piezoelectric elements are driven to form an image. As shown in FIG. 1, current amplification of actuator drive voltage waveform is typically conducted using a bipolar transistor. FIG. 1 shows a typical circuit diagram of a piezoelectric element drive circuit.
In the configuration shown in FIG. 1, base terminals of bipolar transistors Q83 and Q84 constituting a current amplification unit 82 become low (“L”) and an analog switch (SW) 86 is switched ON by a control signal from a recording head controller 81, at which time a voltage +VDD is applied to an actuator 85 actuator charging current A flows to the actuator 85, and a voltage Vcom which is a charged voltage of the actuator 85 flows to ground (GND) as actuator discharge current B.
However, in the conventional current amplification circuit using a bipolar transistor shown in FIG. 1, most of the power to drive the actuator is lost as heat from the bipolar transistor, resulting is wasted power consumption. Although many patent applications disclose configurations to recover the actuator discharge current B of actuator to reuse as the power to drive the actuator (actuator drive power), the recovered power amount is too small because the voltage that recovers the actuator discharge current is too low.
For example, JP-2002-273874-A discloses a configuration to reduce power consumption by effectively using electrical energy accumulated in an actuator, in which actuator discharge current is charged to a capacitor via a constant voltage circuit and the charge charged to the capacitor is reused as charging power for the ground side of the actuator.
However, because the potential at the ground side of the actuator does not change much, only a limited amount of the actuator discharge current can be recovered. Thus, most of the actuator discharge current is still consumed as heat loss from the transistor. Further, in view of a reverse voltage resistance of the transistor in a constant voltage circuit, the potential of capacitor used for charging needs to be set at 5V or so, and thereby most of the power cannot be recovered effectively.